The post-merger gravitational waves from the oscillating remnants of binary neutron star coalescences lie at the high-frequency end of the spectrum, above 2. The post-merger oscillations depend sensitively on the structure and evolution of the hot, hypermassive neutron star remnant, which attains the highest matter densities in the Universe. Given that these signals are likely not detectable with Advanced LIGO and Virgo—even with so-called A+ technology or the proposed Voyager technology [1]}. However, Einstein Telescope, Cosmic Explorer and NEMO [2]}, [3]}, [4]}, [5]} will shed light on unexplored regions of the phase diagram of quantum chromodynamics by delivering reliable post-merger observations.
